Abstract
BackgroundThe activation induced T cell specific adapter protein (TSAd), encoded by SH2D2A, interacts with and modulates Lck activity. Several transcript variants of TSAd mRNA exist, but their biological significance remains unknown. Here we examined expression of SH2D2A transcripts in activated CD4+ T cells and used the SH2D2A variants as tools to identify functionally important regions of TSAd.ResultsTSAd was found to interact with Lck in human CD4+ T cells ex vivo. Three interaction modes of TSAd with Lck were identified. TSAd aa239–256 conferred binding to the Lck-SH3 domain, whereas one or more of the four tyrosines within aa239–334 encoded by SH2D2A exon 7 was found to confer interaction with the Lck-SH2-domain. Finally the TSAd-SH2 domain was found to interact with Lck. The SH2D2A exon 7 encoding TSAd aa 239–334 was found to harbour information essential not only for TSAd interaction with Lck, but also for TSAd modulation of Lck activity and translocation of TSAd to the nucleus. All five SH2D2A transcripts were found to be expressed in CD3 stimulated CD4+ T cells.ConclusionThese data show that TSAd and Lck may interact through several different domains and that Lck TSAd interaction occurs in CD4+ T cells ex vivo. Alternative splicing of exon 7 encoding aa239–334 results in loss of the majority of protein interaction motives of TSAd and yields truncated TSAd molecules with altered ability to modulate Lck activity. Whether TSAd is regulated through differential alternative splicing of the SH2D2A transcript remains to be determined.
Highlights
The activation induced T cell specific adapter protein (TSAd), encoded by SH2D2A, interacts with and modulates Lck activity
We previously observed that TSAd mRNAs SH2D2A-1-4 were expressed in PHA stimulated peripheral blood mononuclear cells [14]
We used reverse transcriptase quantitative PCR assay (RT-PCR) to assess the relative amounts of TSAd transcript variants expressed in primary CD4+ T cells
Summary
The activation induced T cell specific adapter protein (TSAd), encoded by SH2D2A, interacts with and modulates Lck activity. We examined expression of SH2D2A transcripts in activated CD4+ T cells and used the SH2D2A variants as tools to identify functionally important regions of TSAd. When the human genome was sequenced, it was found to contain approximately 35 000 genes [1]. Related proteins encoded by the same gene through alternative transcription may have opposing functions in the cell. Transcription factors may exist as isoforms lacking particular DNA- or protein interacting domains. When such isoforms are expressed, they may inhibit the function of the full length protein [5]. An in silico analysis of the mouse transcriptome revealed that alternative splicing preferentially adds or deletes domains in transcription factors that are important for DNA binding [6]
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